When performing certain procedures on oil and gas wells, such as during workover or intervention operations, running completions, clean-up, abandonment and the like, it is necessary for to apparatus to include valves capable of isolating the formation from surface.
In some instances where a marine riser is utilised to facilitate wellbore operations such as deploying completions or performing wellbore interventions, a so called landing string assembly is typically used, which extends inside the riser from surface to the wellhead, normally landed-out in a wellhead tubing hanger. This landing string may be used as a contained passage to permit fluids and/or equipment to be deployed from surface, and/or may be used to deploy wellbore equipment, such as completion strings, into the associated wellbore.
The landing string is typically includes an upper section composed primarily of tubing, and a lower section which includes various valves for providing well control. For example, landing strings typically include a valve assembly called a subsea test tree (SSTT).
The valves within a SSTT may need to provide the capability to both contain fluids under pressure and also cut obstructions, such as wireline, coiled tubing, tools strings, or the like which extend through the valves. A variety of different valves are used for this so-called “shear and seal” purpose, with the particular type selected dependent on variables such as the wellhead infrastructure and the nature of the wellbore operation.
In many instances landing strings need to be sized and arranged not only to be deployed through a marine riser, but also to be accommodated within wellhead equipment, such as within BOP stacks. For example, the SSTT is typically located within the confines of the BOP, such that the outer dimensions of the SSTT are limited. Also, the axial extent of the SSTT needs to be such that, normally, it must be positioned between individual BOP rams, thus placing axial length size restrictions.
Further, the industry is increasing the requirements for such valves. Notably, emerging specifications such as ISO 13628-7 and API 17G are demanding that the structural integrity of the SSTT, including its housing and associated valves be improved to provide increased fatigue performance. To meet these requirements, the typical arrangement of current valves and actuation hardware takes up an increasing amount of the available space. For in-riser applications, there can be very little room to provide the additional functionality demanded by the industry codes.
Numerous valve designs exist, such as ball valves, flapper valves, ram valves, and the like. Each valve design has associated advantages and disadvantages, and often the particular design selected is very much dependent on the required application.
Ram valves, such as might be used in BOPs, have good cutting and post cut sealing capabilities, but typically require large projecting actuators, which restricts their application, for example precluding the possibility of through riser deployment.
Ball valves can be diametrically compact, and thus permit use in through riser deployment applications. However, used in SSTTs normally have associated internal linear actuators, which requires increased axial length, which can limit their ability to be installed in certain BOP stacks. Also, such internal actuators typically utilise elastomer type seals, which can suffer in the high pressures and temperatures normally associated with wellbores.
The general principles of fluid actuators are described, for example at: http://hydraulicspneumatics.com/200/FPE/MotorsActuators/Article/False/6426/FPE-MotorsActuators. Rotary apparatus is also described in U.S. Pat. Nos. 3,839,945 and 3,680,982 (Jacobellis), 3,229,590 (Huska), 3,137,214 (Feld et al.), 3,977,648 (Sigmon), 3,731,599 (Allen) and 5,975,106 (Morgan et al.). However, such apparatuses are not adapted for use in an SSTT. In addition, inflatable bladders are also described in U.S. Pat. No. 3,975,989 (Hirman), in use in a linear lift apparatus, U.S. Pat. No. 4,751,869 (Paynter) in a tension actuator, and U.S. Pat. No. 5,758,800 (D'ANDRADE) in use to propel water. Industrial bladders are available from Aero Tec Laboratories Ltd of Milton Keynes, or Tompkins Industries Inc. of Olathe, Kans., for use in lift apparatus, motorsports and the like and which are not adapted for use in the oil and gas industry.